Countermeasure method and device for protecting data circulating in an electronic microcircuit

ABSTRACT

The disclosure relates to a countermeasure method in an electronic microcircuit, comprising successive process phases executed by a circuit of the microcircuit, and adjusting a power supply voltage between power supply and ground terminals of the circuit, as a function of a random value generated for the process phase, at each process phase executed by the circuit.

BACKGROUND

1. Technical Field

The present disclosure relates to a countermeasure method for protectingsensitive data circulating in an electronic microcircuit, againstattacks aimed to discover these data. It also relates to a microcircuitportable device such as a chip card, implementing the method.

2. Description of the Related Art

Sensitive data may be in particular encryption or decryption keys, andmore generally cryptographic data used or elaborated duringcryptographic calculations, such as intermediate data of suchcalculations, and identifiers which must be kept secret.

Microcircuit devices using sensitive data are sometimes subjected toattacks which aim is to determine these data. Among the known attacks,the attacks of SPA (Simple Power Analysis) or DPA (Differential PowerAnalysis) type consist in taking numerous current and voltage measurescoming in and going out of the microcircuit during a program executionor data processing by the microcircuit, with different input data. Themeasures obtained are used by a statistical analysis to deduce therefromprotected data, processed or used by the microcircuit. For the same aim,the attacks of EMA (Electromagnetic Analysis) and DEMA (DifferentialElectromagnetic Analysis) type are based on the analysis of theelectromagnetic radiation emitted by the microcircuit.

Attacks by fault injection are also known, which consist in introducingdisturbances into the microcircuit when it executes for examplesensitive algorithms such as cryptographic algorithms, or which aim isto trigger the execution of a downloading routine emitting on a port thedata it memorizes. Such disturbance may be made by applying to themicrocircuit one or more brief lightings for example a laser beam, orone or more voltage peaks to one of the contacts thereof.

So as to fight against these attacks, which are various by nature,numerous solutions, very different from one another, have been brought.The disclosure more particularly relates to those that aim to protectdata circulating in a microcircuit.

Various countermeasure techniques have been implemented so as to fightagainst these attacks. Thus, it is known to perform a logic masking byrandom number consisting in making random data pass through the logiccircuits so as to cause logic gates which are not linked to the data tobe protected to switch. It is also known to introduce random delays intoa synchronous circuit or to implement double rail techniques making itpossible to perform as many logic gates switching to 0 as switching to1.

All these countermeasure techniques reveal to be demanding in terms ofcircuit size, computing speed and electrical consumption. In addition,if these techniques allow the robustness of circuits against attacks tobe improved, they have faults.

BRIEF SUMMARY

One embodiment is a method that protects circuits handling secret dataagainst attacks by signature analysis, without substantially increasingthe complexity or electrical consumption thereof.

Some embodiments relate to a countermeasure method in an electronicmicrocircuit, the method comprising successive process phases executedby a circuit of the microcircuit, the method comprising adjusting apower supply voltage between power supply and ground terminals of thecircuit, as a function of a random value generated for the processphase, at each process phase executed by the circuit, or modulating thepower supply voltage by an alternating signal having an equiprobabledistribution and a period corresponding to the duration of one of moresuccessive process phases.

According to one embodiment, the method comprises: forming themicrocircuit in a substrate, forming in the substrate a wellelectrically isolated from the substrate, forming the power supply orground terminal of the circuit in the isolated well, and at each processphase executed by the circuit, adjusting the voltage between the powersupply and ground terminals of the circuit, in relation to a powersupply voltage of the microcircuit and a ground of the substrate, as afunction of a random value generated for the process phase.

According to one embodiment, adjusting the power supply voltage betweenthe power supply and ground terminals of the circuit is performed in adetermined range as a function of: variations of the power supplyvoltage resulting from variations of the microcircuit performanceslinked to variations of the ambient temperature and variations ofmanufacturing conditions of the microcircuit, variations of the powersupply voltage and ground voltages of the microcircuit as a function ofthe extent of the microcircuit activity, and minimum voltages allowing aswitching of N-channel and P-channel transistors of the microcircuit tobe performed.

According to one embodiment, a bias voltage between the ground terminalof the circuit and a ground terminal of the microcircuit is adjusted asa function of a random value, the voltage difference between a powersupply voltage of the microcircuit and a power supply terminal of thecircuit being fixed.

According to one embodiment, adjusting the power supply voltage betweenthe power supply and ground terminals of the circuit is performed in arange included between −5% to +5% of the power supply voltage of themicrocircuit.

According to one embodiment, the voltage difference between a powersupply terminal of the circuit and a power supply voltage of themicrocircuit is adjusted as a function of a random value, the voltagebetween the ground terminal of the circuit and a ground terminal of themicrocircuit being fixed.

According to one embodiment, adjusting the power supply voltage betweenthe power supply and ground terminals of the circuit is performed in arange included between −5% to +5% around the power supply voltage of themicrocircuit.

According to one embodiment, adjusting the power supply voltage betweenthe power supply and ground terminals of the circuit is performed withan adjusting step between 0.05 to 0.3% of the power supply voltage ofthe microcircuit.

Some embodiments also relate to a microcircuit comprising a circuitexecuting successive process phase, the circuit comprising power supplyand ground terminals and being associated to a power supply circuitconfigured to implement the method such as previously defined.

According to one embodiment, the microcircuit comprises severalcircuits, each comprising power supply and ground terminals and eachassociated to a power supply circuit implementing the method such aspreviously described.

Some embodiments also relate to a microcircuit portable devicecomprising a microcircuit such as previously defined.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Embodiments of the disclosure will be described hereinafter, in relationwith, but not limited to the appended figures wherein:

FIG. 1 schematically shows a cross-section of a substrate in which anintegrated circuit is formed,

FIG. 2 shows on a scale different voltage levels to be considered in ananalysis of the integrated circuit operation,

FIG. 3 is a schematic top view of the integrated circuit, according toone embodiment,

FIG. 4 schematically shows a power supply circuit of the integratedcircuit,

FIG. 5 schematically shows a bias circuit of the integrated circuit,according to one embodiment,

FIG. 6 schematically shows a bias circuit of the integrated circuit,according to another embodiment,

FIG. 7 schematically shows a top view of an integrated circuit,according to another embodiment,

FIG. 8 schematically shows a power supply circuit of the integratedcircuit of FIG. 7.

FIG. 9 is a chip card according to one embodiment of the presentdisclosure.

DETAILED DESCRIPTION

FIG. 1 shows an integrated circuit IC comprising a substrate SUB in asemiconductor material of P-type conductivity in which a circuit ISC isformed. The substrate SUB comprises a P+ doped region SBS forming asubstrate connection connected to a substrate ground SGnd. The circuitISC comprises an embedded well NISO of N-type conductivity and a well NWof N-type conductivity formed in the substrate until reaching the wellNISO. The well NW is formed so as to encircle an area of the substratethus forming a well PW of P-type conductivity. The well PW is thusisolated from the substrate SUB by the wells NISO and NW. The well NISOforms with the well PW a capacitance CIW, and with the substrate SUB acapacitance CIS. The presence of the capacitances CIW, CIS allows thenoise on the ground SGnd of the substrate SUB and the electromagneticradiation emitted by the circuit to be reduced, in particular in theband from 800 MHz to 1 GHz.

The well NW comprises N+ doped regions NS1, NS2 forming well connectionsintended to receive the power supply voltage Vdd of the circuit. Thewell NW also comprises P+ doped regions DP, SP forming the drain and thesource of a P-channel CMOS transistor comprising a gate GP formed abovean area forming the transistor channel, between the source SP and DPregions. The well PW comprises a P+ doped region PWS forming a wellconnection intended to be connected to the ground and two N+ dopedregions SN, DN forming the source and the drain of a N-channel CMOStransistor comprising a gate GN formed above an area between the sourceSN and drain DN regions. Each of the gates GP, GN comprise a conductivelayer overlying a thin dielectric layer on the substrate. The areasbetween a P+ doped region and a N+ doped region comprise a trench filledin with an insulating material (not shown), formed in the substrate toisolate the P+ doped regions from the N+ doped regions. The drain DN, DPand source SN, SP regions of the transistors, form with the wells NW andPW capacitances CPN, CNP. In the example of FIG. 1, the N-channel andP-channel transistors are interconnected so as to form an inverter.Thus, the source SP receives the power supply voltage Vdd, and thesource SN is connected to the ground connection PWS. An input In of theinverter is connected to the gates SN and SP, and an output Out of theinverter is connected to the drains DN, DP.

According to one embodiment, the ground connection PWS of the well PW isnot connected to the substrate ground SGnd, but forms a local groundLGnd of the circuit ISC. The local ground LGnd receives a bias voltageVgb in relation to the substrate ground SGnd, which may be adjusted as afunction of a random value RND between process phases executed by thecircuit ISC. Thus, the circuit ISC is powered by a power supply voltageequal to Vdd−Vgb. Adjusting the bias voltage Vbg of the local groundLGnd may be performed in a range spreading from 0 to a value around 5%of the power supply voltage Vdd of the circuit ISC, for example from 0to 4% of the voltage Vdd.

Such variations of the power supply voltage of the circuit ISC disturbthe statistical analyses made during attacks SPA, EMA, DPA, DEMA whichaim is to discover secret data handled by the circuit ISC.

The maximum extent of the adjusting range of the bias voltage Vgb may bechosen so as to take into account different voltages relative to theintegrated circuit IC operation and features. Thus, the maximum extentof the adjusting range of the bias voltage Vgb may be chosen so as tocomply with the threshold voltages of a N-channel transistor and aP-channel transistor of the integrated circuit IC, with the power supplyvoltage Vdd and with the voltage drops which occur in the circuits ofthe integrated circuit when they are active. The voltages taken intoaccount are considered with an error margin linked to performancevariations of the integrated circuit resulting from ambient temperaturevariations or process corners of the integrated circuit.

FIG. 2 shows on a scale different voltage values and ranges to beconsidered in the integrated circuit IC operation. The scale of FIG. 2comprises, from the top of the scale, voltage ranges GB, VDO, LGO, LGRthen SGO at the bottom of the scale. The voltage range GB delineates thevariations of the power supply voltage Vdd resulting from variations ofthe integrated circuit performances linked to variations of the ambienttemperature and variations of the manufacturing conditions of theintegrated circuit. The voltage range VDO delineates the variations ofthe voltage Vdd as a function of the extent of the integrated circuitactivity. The range VDO corresponds to the drop of the voltage Vdd inthe internal resistors of the integrated circuit. The range LGOdelineates the variations of the bias voltage of the local ground of thecircuit ISC as a function of the extent of the integrated circuit ICactivity. The range LGR delineates the maximum adjusting extent of thebias voltage Vgb of the local ground of the circuit ISC. The range SGOdelineates the variations of the voltage of the substrate SUB ground asa function of the extent of the integrated circuit IC activity.

The width of the range LGR may be chosen so that the voltage differencebetween the ranges VDO and LGO is superior or equal to the sum of theminimum voltages making it possible to guarantee the switching of theN-channel and P-channel transistors of the integrated circuit IC, i.e.,the sum of the threshold voltages Vtn of a N-channel transistor and Vtpof a P-channel transistor, to which an overdrive of around 10% is added.

In the 90 nm integration technology, the rated power supply voltage isof around 1.3 V (with a possible difference of 10%). At the top of thescale of FIG. 2, the ranges GB and VDO have spreads of around 70 mV and50 mV. The spreads of the threshold voltages Vtp and Vtn are on averageof 500 mV and 475 mV. A voltage range of around 1025 mV should thereforebe provided to allow the N-channel and P-channel transistors of thecircuit ISC to switch. The ranges LGO and SGO have spreads of 50 mV and25 mV. Therefore there is around 50 mV (with a possible difference of10%) for the adjusting range LGR of the voltage Vgb. In the 0.18 μmintegration technology, the adjusting range of the voltage Vgb may havean extent of 100 to 200 mV.

According to one embodiment, the value allocated to the bias voltage Vgbmay be randomly chosen among several dozens of different values to avoidan averaging effect, for example with an adjusting step chosen between0.05 and 0.3%. If the adjusting range of the voltage Vgb spreads from 0to 4% of the voltage Vdd, around forty values correspond to an adjustingstep of 0.1% of the voltage Vdd. In the example of the 90 nm integrationtechnology, a step of 0.1% of the voltage Vdd corresponds to around 1.3mV (with a possible difference of 10%).

According to one embodiment, the bias voltage Vgb is randomly modifiedwhen the circuit ISC is in an activation waiting state between twoprocess phases executed by the circuit. This state is for exampledetected by monitoring a “ready” signal supplied by the circuit ISC. Thebias voltage Vgb may also be modified at the beginning of a processphase such as a round of an encryption algorithm for example complyingwith the DES (Digital Encryption System) or AES (Advanced EncryptionSystem) standard. In that case, it may be provided a waiting delaybefore starting the process phase to allow the power supply voltage ofthe circuit ISC to stabilize. It may also be provided to change thevalue of the power supply voltage of the circuit ISC from the end of aprocess phase, i.e., as soon as the circuit is waiting for activation.

According to one embodiment, the bias voltage Vgb may be negative, sothat the adjusting range of the voltage Vgb may spread from around −5 to+5% of the power supply voltage Vdd, for example from −4% to +4% of thepower supply voltage Vdd. The number of adjusting steps may be ofseveral dozens, for example kept at around forty or doubled.

According to another embodiment, the bias voltage may be modulated inthe range from 0 to 5% by an alternating signal, for example sinusoidal,having an equiprobable distribution and a period corresponding to theduration of one or more successive process phases, for example betweensome hundreds of nanoseconds and some microseconds.

FIG. 3 shows the integrated circuit IC, according to one embodiment. InFIG. 3, the integrated circuit IC comprises several circuits formed inthe substrate SUB, several circuits ISC1, ISC2, ISC3 of which may handlesensitive data. The integrated circuit IC comprises a global powersupply circuit GPC supplying to a power supply terminal VS1, VS2, VS3 ofthe various circuits of the integrated circuit, the power supply voltageVdd in relation to the ground of the substrate SGnd, from an externalpower supply voltage Vps.

According to one embodiment, each of the circuits ISC1, ISC2, ISC3comprises an isolated well of P-type conductivity PW1, PW2, PW3encircled by a well of N-type conductivity NW1, NW2, NW3, and isolatedfrom the rest of the substrate SUB by an embedded isolating well NISO1,NISO2, NISO3. The isolated well PW1, PW2, PW3 of each of the circuitsISC1, ISC2, ISC3 comprises a local ground connection LG1, LG2, LG3. Eachcircuit ISC1, ISC2, ISC3 is associated with a bias circuit LGB1, LGB2,LGB3 supplying a bias voltage Vgb1, Vgb2, Vgb3 of the local ground LG1,LG2, LG3 in relation to the ground of the substrate SGnd. Thus, eachcircuit ISC1, ISC2, ISC3 is powered between a power supply terminal VS1,VS2, VS3 receiving the power supply voltage Vdd and the local groundthereof, by a power supply voltage equal to Vdd−Vgb<i> (where i is equalto 1, 2 or 3). Each circuit LGB1, LGB2, LGB3 supplies one of the biasvoltages Vgb1, Vgb2, Vgb3 determined as a function of a random value.Adjusting the bias voltage is made at a time where the circuit ISC1,ISC2, ISC3 is inactive or before a process phase, by providing, ifnecessary, a waiting phase before triggering the process phase, to allowthe power supply voltage (Vdd−Vgb<i>) to stabilize. The inactivity stateis for example detected by monitoring a “ready” signal supplied by thecircuit ISC1, ISC2, ISC3. As the bias voltages Vgb1, Vgb2, Vgb3 of thecircuits ISC1, ISC2, ISC3 are supplied in wells PW1, PW2, PW3 isolatedfrom the substrate SUB by the wells NW1, NW2, NW3 and NISO1, NISO2,NISO3, they may differ at a given time where the circuits ISC1, ISC2,ISC3 are all inactive. Each circuit LGB1, LGB2, LGB3 may therefore haveits own random number generator to adjust its resistor R4.

FIG. 4 shows an example of power supply circuit GPC of the integratedcircuit IC. The circuit GPC comprises two N-channel MOS transistors T1,T2, two resistors R1, R2, a comparator CP and a step-up voltage circuitBPMP. The drain of the transistors T1, T2 receives the external voltageVps. The source of the transistor T1 is linked to the substrate groundSGnd through the resistors R1 and R2 connected in series. The junctionnode ND between the resistors R1, R2 is connected to a direct input ofthe comparator CP. The comparator CP comprises an inverting inputreceiving a constant reference voltage Vref, for example fixed at 0.8 V.The voltage Vref is substantially constant, i.e., in particularindependent of the ambient temperature of the integrated circuit and themanufacture conditions thereof. The voltage Vref may be for examplesupplied by a bandgap reference circuit. The output of the comparator CPis connected to an input of the circuit BPMP. The output of the circuitBPMP is connected to the gates of the transistors T1, T2. The source ofthe transistor T2 supplies the power supply voltage Vdd. The circuitBPMP for example made by a charge pump, supplies a voltage equal to Vdd+Vtn, where Vtn is the threshold voltage of the transistors T1, T2. Thecomparator CP regulates the voltage Vdd by keeping the voltage at thenode ND substantially equal to the voltage Vref. The value of thevoltage Vdd is defined by the values of the resistors R1, R2.

FIG. 5 shows an embodiment of each of the bias circuits LGB1, LGB2,LGB3. In FIG. 5, the circuit LGB comprises two resistors R3, R4, acomparator CP1 and a random number generation circuit RND1. Thecomparator CP1 is powered between the power supply voltage Vdd and thesubstrate ground SGnd. The comparator CP1 receives on an inverting inputa reference voltage Vref. The resistors R3, R4 are connected in seriesbetween the power supply voltage Vdd and the output of the comparatorCP1 which supplies the bias voltage Vgb. The junction node N1 betweenthe two resistors R3, R4 is connected to a direct input of thecomparator CP1. Thus, the comparator CP1 regulates the voltage Vgb sothat the voltage at the node N1 is kept equal to the reference voltageVref. The voltage Vgb supplied by the circuit LGB may therefore becalculated using the following equation:

Vgb=Vref−(Vdd−Vref)R4/R3   (1)

One of the two resistors, for example the resistor R4 may be adjustableand controlled by the generator RND1, to adjust the bias voltage Vgb. Inthe 90 nm technology with the power supply voltage Vdd fixed at 1.3 V,and if Vref is fixed at 0.8 V and if Vgb varies between 0 and 50 mV,then the ratio R4/R3 of the values of the resistors R4 and R3 isadjustable between 1.6 and 1.5.

Conventionally, the adjustable resistor R4 may be made using severalresistors connected in series, a switch being mounted in parallel toeach resistor mounted in series. Each switch is controlled by a bit of arandom word supplied by the generator RND1. To respect theequibrobability of the value allocated to the voltage Vgb, the resistorsconstituting the variable resistor may have as respective values forexample R, 2R, 4R, 8R, . . . .

FIG. 6 shows another embodiment of each of the bias circuits LGB1, LGB2,LGB3. In FIG. 6, the circuit LGB′ comprises a resistor R5, a comparatorCP2, a current source CS and a random number generation circuit RND2.The current source CS is powered by the voltage Vdd and supplies acurrent Iref equal to the reference voltage Vref divided by a resistorR6 (not shown). The comparator CP2 is powered between the power supplyvoltage Vdd and the substrate ground SGnd. The resistor R5 is connectedin series between the current source CS and the ground. The junctionnode N2 between the current source and the resistor R5 is connected to adirect input of the comparator CP2. The output of the comparator CP2which supplies the bias voltage Vgb is looped on the inverting inputthereof. Thus, the comparator CP2 regulates the voltage Vgb by keepingit equal to the voltage at the node N2. The voltage Vgb supplied by thecircuit LGB may therefore be calculated using the following equation:

Vgb=R5Iref=Vref−R5/R6   (2)

In relation to the circuit LGB, the circuit LGB′ has the advantage ofnot being sensitive to variations of the power supply voltage Vdd whichmay occur in particular when the integrated circuit IC is active due tovoltage drops in the internal resistors of the circuit IC.

The resistor R5 may be adjustable and controlled by the generator RND2,to adjust the bias voltage Vgb. In the 90 nm technology with the powersupply voltage Vdd fixed at 1.3 V, and if Vref is fixed at 0.1 V and ifVgb is adjustable between 1 mV and 50 mV, then the ratio R5/R6 of thevalues of the resistors R5 and R6 is adjustable between 1/100 and 1/2.

FIG. 7 shows an integrated circuit, according to another embodiment. InFIG. 7, the integrated circuit IC1 comprises several circuits formed inan N-conductivity substrate SUB1, including some circuits ISC11, ISC12,ISC13 handling sensitive data, such as secret data. The integratedcircuit IC1 comprises a substrate ground Gnd, and receives an externalpower supply voltage Vps.

According to one embodiment, each of the circuits ISC1, ISC2, ISC3comprises a well of N-type conductivity NW11, NW12, NW13 encircled by awell of P-type conductivity PW1, PW2, PW3, and isolated from the rest ofthe substrate SUB1 by an embedded isolating well PIS11, PIS12, PIS13.Each of the circuits ISC11, ISC12, ISC13 comprises a power supplyterminal VS1, VS2, VS3 connected to a power supply circuit LPC1, LPC2,LPC3 supplying to the power supply terminal a power supply voltage Vdl1,Vdl2, Vdl3 different from the power supply voltage Vps. Thus, eachcircuit ISC11, ISC12, ISC13 is powered by the power supply terminalVdl<i> (where i is equal to 1, 2 or 3). Each of the power supplyvoltages Vdl1, Vdl2, Vdl3 is adjusted as a function of a random value,so as to mask the activity of the circuit with regards to an attackwhich aim is to discover the data handled by the circuit. Adjusting thepower supply voltage Vdl<i> of each circuit ISC11, ISC12, ISC13 is madeat a time where the circuit is inactive or before a process phase, forexample at the end of a process phase.

FIG. 8 shows an example embodiment of one of the bias circuits LPC1,LPC2, LPC3. In FIG. 8, the circuit LPC comprises two N-channel MOStransistors T4, T5, two resistors R7, R8, a comparator CP3, a voltagestep up circuit BPM3 and a random number generation circuit RND3. Thedrain of the transistors T4, T5 receives the power supply voltage Vps.The source of the transistor T4 is linked to the substrate ground Gndthrough the resistors R7 and R8 connected in series. The junction nodeN3 between the resistors R7, R8 is connected to a direct input of thecomparator CP3. The comparator CP3 comprises an inverting inputreceiving a constant reference voltage Vref, for example fixed at 0.8 V.The output of the comparator CP3 is connected to an input of the circuitBPM3. The output of the circuit BPM3 is connected to the gates of thetransistors T4, T5. The source of the transistor T5 supplies the powersupply voltage Vdl of one of the circuits ISC11, ISC12, ISC13. Thecomparator CP3 regulates the voltage Vdl by keeping the voltage at thenode N3 substantially equal to the voltage Vref. The value of thevoltage Vdl is defined by the values of the resistors R7, R8. One of thetwo resistors R7, R8, for example the resistor R7 is adjustable andcontrolled by the circuit RND3. Thus, the comparator CP3 regulates thevoltage Vdl which depends on the values of the resistors R7, R8, so thatthe voltage at the node N3 is kept equal to the reference voltage Vref.

Here again, adjusting the local power supply voltage Vdl may beperformed in a range from 100% to a value around 95% of the power supplyvoltage Vps of the integrated circuit IC1, for example from 100 to 96%of the voltage Vps.

According to one embodiment, the power supply voltage Vdl may beadjusted in an adjusting range which may spread from around −5 to +5% ofthe power supply voltage Vps, for example from −4% to +4% around thepower supply voltage Vps. The number of adjusting steps may be ofseveral dozens, for example kept at around forty or doubled.

The maximum width of the adjusting range of the bias voltage Vdl may bechosen so as to comply with the sum of the threshold voltages of aN-channel transistor and a P-channel transistor of the integratedcircuit IC, at the power supply voltage Vps and the voltage drops whichoccur in the circuits when they are active, formed in the substrate andthe wells, these voltage values being considered with an error marginlinked to performance variations of the integrated circuit resultingfrom ambient temperature variations or process corners of the integratedcircuit. In the 90 nm integration technology, the rated value of thepower supply voltage Vps is of around 1.3 V (with a possible differenceof 10%). Adjusting the power supply voltage Vdl may be performed in arange between Vps or Vps+50 mV to around Vps−50 mV (with a possibledifference of 10%). In the 0.18 μm integration technology, the adjustingrange of the voltage Vdl may extend from a value comprised between Vpsand Vps+200 mV to a value comprised between Vps−100 and Vps−200 mV.

According to one embodiment, the value allocated to the power supplyvoltage Vdl may be chosen among several dozens of different values toavoid an averaging effect, for example with an adjusting step chosenbetween 0.05 and 0.3%. If the adjusting range of the voltage Vdl spreadsfrom 100% to 96%, around forty values correspond to an adjusting step of0.1%.

According to one embodiment, the power supply voltage Vdl is randomlymodified when the circuit ISC11, ISC12, ISC13 is inactive or before aprocess phase, by providing, if necessary, a waiting phase beforetriggering the process phase, to allow the power supply voltage (Vdl<i>)to stabilize. This state is for example detected by monitoring a “ready”signal supplied by the circuit ISC11, ISC12, ISC13. The power supplyvoltage Vdl may also be modified at the beginning of a process phase. Inthat case, it may be provided a waiting delay before starting theprocess phase to allow the power supply voltage Vdl to stabilize. As thepower supply voltages Vdl1, Vdl2, Vdl3 of the circuits ISC11, ISC12,ISC13 are supplied in wells NW1, NW2, NW3 isolated from the substrateSUB by the wells PW1, PW2, PW3 and PIS11, PIS12, PIS13, they may differat a given time where the circuits ISC11, ISC12, ISC13 are all active.Each circuit LPC1, LPC2, LPC3 may therefore have its own random numbergenerator to adjust its resistor R7.

It will be clear to those skilled in the art that the present disclosureis susceptible of various embodiments and applications. Thus, thedisclosure is not limited to a microcircuit comprising several circuitsindependently powered. The disclosure also applies to a microcircuit inwhich the whole power supply voltage is randomly adjusted at thebeginning of a process phase. The power supply terminals of themicrocircuit are therefore not necessarily formed in a well isolatedfrom the rest of the substrate in which the microcircuit is formed.

In addition, if in the examples described, the voltage at the powersupply terminal VG1, VG2, VG3 of one of the circuits ISC1, ISC2, ISC3 isequal to the power supply voltage Vdd of the integrated circuit, or ifthe voltage of the local ground LG1, LG2, LG3 of one of the circuitsISC11, ISC12, ISC13 is equal to that of the ground Gnd of the integratedcircuit, admittedly, a constant voltage difference may be appliedbetween these voltages without going out of the frame of the presentdisclosure.

A microcircuit portable device according to one embodiment is shown inFIG. 9. In particular, the microcircuit portable device is a chip cardCC that includes a support S that typically would be made of plastic, asis typical for chip cards. The chip card CC also includes an integratedcircuit such as one of the integrated circuits IC, IC1 described above.Those skilled in the art will understand that a microcircuit portabledevice according to the present disclosure can be implemented using anyportable device with a processor that is desired to be protected fromhacking attempts.

The various embodiments described above can be combined to providefurther embodiments. These and other changes can be made to theembodiments in light of the above-detailed description. In general, inthe following claims, the terms used should not be construed to limitthe claims to the specific embodiments disclosed in the specificationand the claims, but should be construed to include all possibleembodiments along with the full scope of equivalents to which suchclaims are entitled. Accordingly, the claims are not limited by thedisclosure.

1. A method of making an electronic microcircuit, comprising: forming a processing circuit configured to execute successive process phases, the forming including: forming in a substrate an isolated well electrically isolated from an underlying portion of the substrate; and forming a power supply terminal and a ground terminal of the processing circuit, wherein at least one of the power supply and ground terminals is formed in the isolated well; and forming a power supply circuit configured to, for each of the processing phases, adjust a power supply voltage between the power supply and ground terminals of the processing circuit as a function of a varying signal.
 2. A method according to claim 1, wherein forming the power supply circuit includes forming the power supply circuit configured to: detect inactive phases between the successive active phases; and adjust the power supply voltage as a function of the varying signal in response to detecting the inactive phases.
 3. A method according to claim 1, wherein forming the power supply circuit includes forming the power supply circuit configured to adjust the power supply voltage between the power supply and ground terminals of the processing circuit in a determined range as a function of: variations of the power supply voltage resulting from variations of performances of the processing circuit linked to variations of an ambient temperature and variations of manufacturing conditions of the microcircuit, variations of the power supply voltage and ground voltages of the microcircuit as a function of an extent of activity of the microcircuit, and minimum voltages allowing a switching of N-channel and P-channel transistors of the microcircuit to be performed.
 4. A method according to claim 1, wherein forming the power supply circuit includes forming the power supply circuit configured to adjust a bias voltage between the ground terminal of the circuit and a ground terminal of the microcircuit as a function of a random value, a voltage difference between a power supply voltage of the microcircuit and the power supply terminal of the processing circuit being fixed.
 5. A method according to claim 4, wherein forming the power supply circuit includes forming the power supply circuit configured to adjust the power supply voltage between the power supply and ground terminals of the processing circuit is performed in a range included between −5% to +5% of the power supply voltage of the microcircuit.
 6. A method according to claim 1, wherein forming the power supply circuit includes forming the power supply circuit configured to adjust the voltage difference between a power supply terminal of the processing circuit and a power supply voltage of the microcircuit as a function of a random value while a voltage between the ground terminal of the processing circuit and a ground terminal of the microcircuit is fixed.
 7. A method according to claim 6, wherein forming the power supply circuit includes forming the power supply circuit configured to adjust the power supply voltage between the power supply and ground terminals of the processing in a range included between −5% to +5% around the power supply voltage of the microcircuit.
 8. A method according to claim 1, wherein forming the power supply circuit includes forming the power supply circuit configured to adjust the power supply voltage between the power supply and ground terminals of the processing circuit with an adjusting step from 0.05 to 0.3% of the power supply voltage of the microcircuit.
 9. A method according to claim 1, wherein the varying signal is a randomly varying signal.
 10. A method according to claim 1, wherein the varying signal is an alternating signal having an equiprobable distribution and a period corresponding to a duration of one of more successive process phases.
 11. A microcircuit comprising: a first processing circuit configured to execute first successive process phases and including power supply and ground terminals, wherein at least one of the power supply and ground terminals is formed in an isolated well of a substrate, the isolated well being electrically isolated from an underlying portion of the substrate; and a first power supply circuit coupled to the first processing circuit and configured to, for each of the processing phases, adjust a power supply voltage between the power supply and ground terminals of the processing circuit as a function of a first varying signal.
 12. A microcircuit according to claim 11, comprising: a second processing circuit configured to execute second successive process phases and including power supply and ground terminals; and a second power supply circuit configured to, for each of the second successive processing phases, adjust a power supply voltage between the power supply and ground terminals of the second processing circuit as a function of a second varying signal.
 13. A microcircuit according to claim 11, wherein the first power supply circuit includes: a comparator having first and second input terminals and an output terminal, the first input terminal being configured to receive a reference voltage; first and second resistors coupled between the power supply terminal and the output terminal of the comparator, the first resistor being a variable transistor with a control terminal, and the first and second resistors being coupled to each other at the second input terminal of the comparator; and a random signal generator coupled to the control terminal of the first resistor and configured to generate a random signal to randomly vary a resistance of the first resistor.
 14. A microcircuit according to claim 11, further comprising: microcircuit power supply and ground terminals, wherein the first power supply circuit includes: a comparator having first and second input terminals and an output terminal, the second input terminal being coupled to the output terminal; a variable resistor and a current source coupled between the microcircuit power supply and ground terminals, the variable resistor having a control terminal, and the variable resistor and current source being coupled to each other at the first input terminal of the comparator; and a random signal generator coupled to the control terminal of the variable resistor and configured to generate a random signal to randomly vary a resistance of the variable resistor.
 15. A microcircuit according to claim 11, further comprising: microcircuit power supply and ground terminals, wherein the first power supply circuit includes: a comparator having first and second input terminals and an output terminal, the first input terminal being coupled to the output terminal; a first resistor, a second resistor, and a first transistor coupled in series between the microcircuit power supply and ground terminals, the first resistor being a variable transistor with a control terminal, and the first and second resistors being coupled to each other at the second input terminal of the comparator, the first transistor having a control terminal; a random signal generator coupled to the control terminal of the variable resistor and configured to generate a random signal to randomly vary a resistance of the variable resistor; a second transistor coupled between the microcircuit power supply terminal and the power supply terminal of the first processing circuit, the second transistor having a control terminal; and a voltage step up circuit coupled between the output of the comparator and the control terminals of the first and second transistors.
 16. A microcircuit according to claim 11, wherein the first power supply circuit is configured to detect inactive phases between the successive active phases of the first processing circuit and adjust the power supply voltage between power supply and ground terminals of the first processing circuit, as a function of the varying signal during the inactive phases between the successive process phases of the first processing circuit, in response to detecting the inactive phases.
 17. A microcircuit portable device, comprising: a support; and a microcircuit carried by the support and including: a first processing circuit configured to execute first successive process phases and including power supply and ground terminals, wherein at least one of the power supply and ground terminals is formed in an isolated well of a substrate, the isolated well being electrically isolated from an underlying portion of the substrate; and a first power supply circuit coupled to the first processing circuit and configured to, for each of the processing phases, adjust a power supply voltage between the power supply and ground terminals of the processing circuit as a function of a first varying signal.
 18. A microcircuit portable device according to claim 17, wherein the microcircuit includes: a second processing circuit configured to execute second successive process phases and including power supply and ground terminals; and a second power supply circuit configured to, for each of the second successive processing phases, adjust a power supply voltage between the power supply and ground terminals of the second processing circuit as a function of a second varying signal.
 19. A microcircuit portable device according to claim 17, wherein the first power supply circuit includes: a comparator having first and second input terminals and an output terminal, the first input terminal being configured to receive a reference voltage; first and second resistors coupled between the power supply terminal and the output terminal of the comparator, the first resistor being a variable transistor with a control terminal, and the first and second resistors being coupled to each other at the second input terminal of the comparator; and a random signal generator coupled to the control terminal of the first resistor and configured to generate a random signal to randomly vary a resistance of the first resistor.
 20. A microcircuit portable device according to claim 17, wherein the microcircuit includes: microcircuit power supply and ground terminals, wherein the first power supply circuit includes: a comparator having first and second input terminals and an output terminal, the second input terminal being coupled to the output terminal; a variable resistor and a current source coupled between the microcircuit power supply and ground terminals, the variable resistor having a control terminal, and the variable resistor and current source being coupled to each other at the first input terminal of the comparator; and a random signal generator coupled to the control terminal of the variable resistor and configured to generate a random signal to randomly vary a resistance of the variable resistor.
 21. A microcircuit portable device according to claim 17, wherein the microcircuit includes: microcircuit power supply and ground terminals, wherein the first power supply circuit includes: a comparator having first and second input terminals and an output terminal, the first input terminal being coupled to the output terminal; a first resistor, a second resistor, and a first transistor coupled in series between the microcircuit power supply and ground terminals, the first resistor being a variable transistor with a control terminal, and the first and second resistors being coupled to each other at the second input terminal of the comparator, the first transistor having a control terminal; a random signal generator coupled to the control terminal of the variable resistor and configured to generate a random signal to randomly vary a resistance of the variable resistor; a second transistor coupled between the microcircuit power supply terminal and the power supply terminal of the first processing circuit, the second transistor having a control terminal; and a voltage step up circuit coupled between the output of the comparator and the control terminals of the first and second transistors.
 22. A microcircuit portable device according to claim 17, wherein the first power supply circuit is configured to detect inactive phases between the successive active phases of the first processing circuit and adjust the power supply voltage between power supply and ground terminals of the first processing circuit, as a function of the varying signal during the inactive phases between the successive process phases of the first processing circuit, in response to detecting the inactive phases. 